Meta-analysis of welfare, egg quality, production and selected behavioural traits to evaluate small group housing systems for laying hens

The objective of the current investigation was to employ the tool of meta-analysis in order to assess selected welfare, behavioural and production traits of four different layer strains kept in different types of housing systems. The study was carried out from 1999 to 2006 at two experimental farms and included data of ten laying periods, comprising 4,553 hens in total. Data were collected by the different authors employing fully identical methods. Housing systems tested were conventional cages, two types of furnished cages, small group systems, an aviary housing system and an intensive free range system. Least square means (LSM) of bone strength, keel bone status, foot pad health, plumage condition, egg shell strength, production, mortality and selected behavioural patterns were chosen for meta-analysis. LSM were weighted with their squared reciprocal standard errors and meta-analysis was carried out using a linear weighted least square model. Housing system had a significant effect on humerus and tibia bone strength, hyperkeratosis of sole pad, production, mortality rate and dustbathing on wire floor. At the expense of inferior keel bone status compared to furnished cages and unfavourable production and mortality rate, bone strength of hens kept in the aviary system could not be exceeded by any other type of housing system tested. Foot pad health of hens kept in the aviary was not found to be unfavourable although litter had been provided and hyperkeratosis of sole pad was found to be mostly prevalent in the small group systems. Highest production and lowest mortality rates were detected in furnished cages and small group systems. Humerus bone strength, keel bone status, plumage condition, eggshell strength, mortality rate and the selected behavioural patterns, except the traits dust bathing on wire floor and standing/sitting on perch, did not differ between hens kept in furnished cages and small group systems.

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